If I had to kill & eat live rats (that can bite back hard-! in self-defense) by ONLY wrapping my mouth & body around it, I'd be afraid too!
Snakes get hurt when fed live...sooner or later it happens, whether or not YOU noticed. Then they can lose their "nerve"...
I know how HARD it is to entice a BP to accept f/t or fresh-killed* prey, but it's best that you learn. *have you even TRIED fresh-killed (& still warm or heat-enhanced)
rats?